The present invention relates to an ignition device for internal combustion engines and, more particularly, to a high-energy ignition device in which the output from a DC-DC converter is superposed on the discharge current through a spark plug such as to attain a long duration of the discharge in the spark plug.
An ignition device allows a high voltage discharge between two electrodes of a spark plug so as to ignite a mixture in the engine, thereby triggering an explosive combustion. In order to attain a higher fuel economy and higher output power, it is necessary to effect stable and efficient combustion of the mixture.
A high voltage on the order of 10 to 20 KV is required for breaking the insulation across the electrode gap in the spark plug. However, once the insulation is broken, the discharge can be maintained with only a medium-high voltage of 1 to 2 KV.
In view of this fact, a proposal has been made in which a high voltage pulse, generated by an ignition coil, is initially applied to break the insulation in the spark plug and, after the breakage of the insulation, a medium-high voltage generated by a DC-DC converter is superposed on the discharge current, to thereby maintain the discharge for a longer time. This ignition device, however, requires complicated wiring for connecting three constituent elements: namely an IC igniter, ignition coil and a DC-DC converter. It is quite troublesome to find sufficient room for accommodating these components and wiring in the restricted space of the engine compartment.
An object of the invention is to provide a high-energy ignition device which permits simplification of the wiring and reduces the overall size of the device.
To this end, according to the invention, there is provided a high-energy ignition device in which a spark plug and an output transformer of a DC-DC converter are subjected to an insulation treatment and, after laying electric connection between major portions, the spark plug and the DC-DC converter are integrated with forming resin such as to withstand vibration while maintaining necessary insulation of the spark plug and the output transformer of the DC-DC converter.